12.3 Anaerobic Respiration

2026 Syllabus Objectives

  1. Describe anaerobic respiration as the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen
  2. State that anaerobic respiration releases much less energy per glucose molecule than aerobic respiration
  3. State the word equation for anaerobic respiration in yeast as: glucose → alcohol + carbon dioxide
  4. State the word equation for anaerobic respiration in muscles during vigorous exercise as: glucose → lactic acid
  5. State the balanced chemical equation for anaerobic respiration in yeast as: C6H12O6→2C2H5OH+2CO2\mathrm{C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2}
  6. State that lactic acid builds up in muscles and blood during vigorous exercise causing an oxygen debt
  7. Outline how the oxygen debt is removed after exercise, limited to: (a) continuation of fast heart rate to transport lactic acid in the blood from the muscles to the liver (b) continuation of deeper and faster breathing to supply oxygen for aerobic respiration of lactic acid (c) aerobic respiration of lactic acid in the liver

What is Anaerobic Respiration? 🔋

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Anaerobic respiration is a type of cellular respiration that occurs when oxygen is not available or is in limited supply. It involves chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.

Key Characteristics ⚡

  • Occurs in the cytoplasm of cells (not in mitochondria)
  • Does not require oxygen
  • Releases much less energy per glucose molecule than aerobic respiration
  • Produces different waste products depending on the organism

Important: Anaerobic respiration is less efficient than aerobic respiration because glucose is not completely broken down, so less energy is released from each glucose molecule.

Anaerobic Respiration in Different Organisms

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1. Anaerobic Respiration in Yeast 🍞

In yeast and some other microorganisms, anaerobic respiration produces ethanol (alcohol) and carbon dioxide.

Word equation:

glucose→alcohol + carbon dioxide\text{glucose} \rightarrow \text{alcohol + carbon dioxide}

Balanced chemical equation:

C6H12O6→2C2H5OH+2CO2\mathrm{C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2}

Where:

  • C6H12O6\mathrm{C_6H_{12}O_6} = glucose
  • C2H5OH\mathrm{C_2H_5OH} = ethanol (alcohol)
  • CO2\mathrm{CO_2} = carbon dioxide

Applications:

  • This process is used in brewing (making alcoholic drinks)
  • Used in baking (carbon dioxide makes bread rise)

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